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Caracterização experimental do comportamento mecânico sob solicitação multiaxial em junções de chapas AA2024-T3 soldadas por fricção-mistura ('FSW').; Experimental characterization of the mechanical behaviour under multiaxial loads of AA2024-T3 sheets welded by friction stir welding (FSW).

Cerveira, Renato Luiz Lehnert Portela
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/09/2008 PT
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Este trabalho tem o intuito de analisar a junção realizada pelo processo de soldagem por fricção-mistura (FSW) pelo do teste de Arcan. É apresentada inicialmente uma revisão bibliográfica dos estudos já realizados nessa área e da teoria relevante. Foram realizados ensaios para avaliar a falha da junta sob carregamento multiaxial quando comparada à falha do material base. Para a realização dos ensaios utilizouse uma máquina de tração com capacidade de 50 kN. Foi projetado e construído um dispositivo de Arcan modificado, que permite a variação do ângulo com o qual a força de tração é aplicada. Os resultados práticos demonstraram as características de resistência da junção por FSW quando sujeita à forças de tração e cisalhamento. Os resultados obtidos servem como base para comparação entre junções feitas por FSW e por métodos convencionais como a utilização de rebites (prática muito comum na indústria aeronáutica).; The aim of this work is to analyze the junction made by Friction Stir Welding (FSW) using the Arcan test. Initially is presented a review of the studies carried out in this area and the relevant theory for the project. Tests were executed in order to evaluate the failure of the welding under multiaxial loading when compared to the failure of the base material. In order to execute the Arcan Tests...

Identificação de bactérias isoladas de elementos metálicos de torres de transmissão de energia elétrica e avaliação de resistência à metais pesados.; Identification of bacteria isolated from metallic elements of electric energy transmission towers and evaluation of heavy metal resistance.

Silva, Bárbara Pereira da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 13/07/2011 PT
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A corrosão metálica é um problema que afeta a economia mundial, sendo responsável pelo aumento dos custos de geração, transmissão e distribuição de energia elétrica e pode ser influenciada por atividades microbianas, podendo levar a aceleração ou inibição do processo. O presente trabalho teve por objetivo isolar e identificar as bactérias associadas a processos de corrosão em torres de transmissão de energia, bem como avaliar a resistência destas bactérias a diferentes metais pesados buscando selecionar micro-organismos com potencial para biorremediação. A identificação taxonômica dos isolados associados a elementos metálicos foi efetuada por análise filogenética das sequências parciais do gene RNA ribossomal 16S, resultando em 101 bactérias distribuídas em oito gêneros: Lysinibacillus, Serratia, Stenotrophomonas, Pseudomonas, Exiguobacterium, Chryseobacterium, Bacillus e Acinetobacter. Todos os gêneros foram resistentes a mais de um metal, sendo que o metal que menos afetou o crescimento dos isolados foi o cromo e o que mais afetou foi o mercúrio.; Metallic corrosion is a problem that affects the world economy, being responsible for the increased costs of generating, transmission and distribution of electricity and can be influenced by microbial activities...

Proposta de um sistema de avaliação geoambiental para rios: estudo de caso para o Córrego das Cruzes (Santo Antonio do Aracanguá/SP); Proposal of a geoenvironmental evaluation system for rivers: study of case for Córrego das Cruzes stream (Santo Antonio do Aracanguá/ SP)

Albuquerque Sobrinho, Edwardo José de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 04/03/2013 PT
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Os rios, enquanto produtos da interação entre os agentes internos e externos da Terra, são elementos da paisagem em constante mutação ao longo do tempo e do espaço, sujeitos aos fenômenos da erosão e da sedimentação (assoreamento). Contudo, o homem ao interagir de forma negligente com o meio, no caso, os diferentes cursos de água, intensifica o processo natural de degradação ambiental. Estes impactos variam de lugar para lugar, em função de diferentes fatores, dentre eles o clima, o tipo de solo, resistência geomecânica dos materiais, condições geomorfológicas e estruturais da drenagem, entre outros. Por conta disto, este trabalho propõe um sistema de avaliação geoambiental para rios, cuja aplicação ocorreu em um curso d´água de segunda ordem, localizado na porção noroeste do Estado de Estado de São Paulo, com área de 7,81 'KM POT.2'. O desenvolvimento deste sistema deu-se a partir da compartimentação de sete grupos distintos (Climático, geomorfológico, geológico, hidráulico, físico-químico para água e sedimentos, biológico e uso e ocupação, contendo 33 parâmetros). A atribuição dos pesos teve como base, o potencial que uma determinada variável tem em contribuir no processo degradação ambiental...

Influence of grinding on the roundness, residual stresses and microstructure of VC131 steel analysed by varying the type of cutting fluid

Catai, Rodrigo Eduardo; Bianchi, Eduardo Carlos; de Sampaio Alves, Manoel Cléber; de Aguiar, Paulo Roberto
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica
ENG
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This paper by R. E. Catai, E. C. Bianchi, P. R de Águia and M. C. Alves reports on the results of an analysis made of roundness errors, residual stresses, and SEM micrographs of VC131 steel. The analysis involved workpieces ground with two types of cutting fluid: synthetic cutting fluid and emulsive oil. In this study, the cutting parameters were kept constant while the type of cutting fluid was varied. The amount of cutting fluid injected in the process was also varied, aiming to identify the ideal amount required to obtain good results without causing structural damage to the workpiece. The SEM analyses of roundness errors and residual stresses revealed that, of the two cutting fluids, emulsive oil provided better tensions due to its greater lubricating power.

Evolução temporal da resistencia mecanica em laboratorio, de misturas simulando a reciclagem de pavimento asfaltico com adição de cimento portland; Temporal evolution of mechanical resistance in laboratory, of mixtures simulating asphalt pavement recycling with portland cement additions

Claudia Betine Gusmão
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/12/2008 PT
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O presente trabalho visa estudar o processo de reciclagem de pavimento asfaltico com cimento Portland, atraves da analise de metodo de reciclagem, equipamentos utilizados, procedimentos empregados em campo, alem do estudo das vantagens e desvantagens do uso da reciclagem em pavimentos asfalticos. O trabalho trata ainda de uma forma detalhada o pavimento asfaltico com adicao de cimento Portland, atraves de ensaios tecnologicos simulando em laboratorio, para diferentes dosagens o comportamento mecanico em funcao do tempo do material obtido em campo.; This work studies the process of asphalted pavement recycling with cement Portland additive through the analysis of recycling method, equipments and procedures used in the field, in addition to studying the advantages and disadvantages of the use of recycling in asphalted pavement. The work also approaches in detail the recycled asphalt pavement with Portland cement additive, through technological tests through laboratory simulation, to different dosage and the analysis of mechanical behavior through time of that material obtained in field

Physics of strength and plasticity.

Fonte: MIT Press Publicador: MIT Press
Formato: xxv, 404 p.; 58090195 bytes; application/pdf
EN_US; ENG
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Edited by Ali S. Argon.; Published in honor of Egon Orowan.; Includes bibliographies.

Pitting and crack initiation in high strength aluminum alloys for aircraft applications

Au, Hiu
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 142 leaves; 12186489 bytes; 12186249 bytes; application/pdf; application/pdf
ENG
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by Hiu Au.; Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.; Includes bibliographical references (leaves 136-142).

Chemistry directed assembly of multilayered polymer thin films and colloidal particles

Jiang, Xueping, 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 246 p.; 22612814 bytes; 22612572 bytes; application/pdf; application/pdf
ENG
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In this thesis, multilayered polymer thin films have been directed to different regions of a surface based on both electrostatic and secondary interactions between the polymer and the surface. This concept of adsorption directed by surface chemistry is universal, in that the same sets of rules derived for polymeric systems can also be applied to molecule and meso-scale systems, including dye molecules, colloidal particles, proteins and cells. An approach of "surface sorting" was proposed to direct two or more objects with varying functionalities to deposit on predetermined regions of a surface based on specific surface interactions. Specifically, on the surface patterned with alternating charged carboxylic acid (COOH) surface groups and neutral oligoethylene glycol (EG) surface groups, linear polyethyleneimine (LPEI) based multilayers predominately adsorb on the COOH surface, with maximal selectivity at the moderate pH level of 4.8; in contrast, polyallylamine hydrochloride (PAH) based multilayers are attracted to the EG surface under certain pH conditions, with maximal selectivity on EG also at a pH of 4.8. Chemical force microscopy was used to directly examine the intermolecular interactions between polyamines and functional surfaces. The driving forces were identified to be primarily an electrostatic interaction for LPEI adsorption on the COOH surface...

Chemical, mechanical, and thermal control of substrate-bound carbon nanotube growth

Hart, Anastasios John, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 357 p.
ENG
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Carbon nanotubes (CNTs) are long molecules having exceptional properties, including several times the strength of steel piano wire at one fourth the density, at least five times the thermal conductivity of pure copper, and high electrical conductivity and current-carrying capacity. This thesis presents methods of CNT synthesis by atmospheric-pressure thermal chemical vapor deposition (CVD), where effective choice of the catalyst composition and processing conditions enables growth of tangled single-wall CNTs or structures of aligned multi-wall CNTs, on bare silicon, microstructured silicon, and ceramic fibers. Applying mechanical pressure during growth controls the structure of a CNT film while causing significant defects in the CNTs. This mechanochemisty approach is used to "grow-mold" CNTs into 3D-shaped microforms. A new reactor apparatus featuring a resistively-heated suspended platform enables rapid ( 100 °C/s) temperature control and versatile in situ characterization, including laser measurement of CNT film growth kinetics, and imaging of stress-induced film cracking. By thermally pre-treating the reactant mixture before it reaches the substrate platform, aligned CNTs are grown to 3 mm length in just 15 minutes.; (cont.) A microchannel array is created for combinatorial flow studies of nanomaterials growth...

The design and analysis of tension fabric structures

Son, Miriam Euni
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 48 leaves
ENG
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Although tensioned fabric structures are increasingly in demand, since they are comparatively new to the engineering world, there are relatively limited resources available about such structures. This report reviews the topics that encompass the design and analysis of tensioned fabric structures. First, an overview of the conceptual basis of tensioned membranes is discussed, as well as the different shapes that are formed using manipulations of the basic concept. Since the material properties play a key role in the durability of tension fabric structures, the ideal material characteristics, as well as the current available fabrics are described. Both the strength of the employed materials and the load considerations for design are outlined. The report follows by explaining the process of roughly assessing the scope of a project, as well as the variety of non-linear analysis that must be performed and the methods used to perform them. This report concludes with key connection details that must be considered for a successful tension fabric structure.; by Miriam Euni Son.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.; Includes bibliographical references (leaf 48).

Design of a high-speed, meso-scale nanopositioners driven by electromagnetic actuators

Golda, Dariusz, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 261 p.
ENG
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The purpose of this thesis is to generate the design and fabrication knowledge that is required to engineer high-speed, six-axis, meso-scale nanopositioners that are driven by electromagnetic actuators. When compared to macro-scale nanopositioners, meso-scale nanopositioners enable a combination of greater bandwidth, improved thermal stability, portability, and capacity for massively parallel operation. Meso-scale nanopositioners are envisioned to impact emerging applications in data storage and nanomanufacturing, which will benefit from low-cost, portable, multi-axis nanopositioners that may position samples with nanometer-level precision at bandwidth of 100s of Hz and over a working envelope greater than 10x10x10 micrometers3 This thesis forms the foundation of design and fabrication knowledge required to engineer mesoscale systems to meet these needs.The design combines a planar silicon flexure bearing and unique moving-coil microactuators that employ millimeter-scale permanent magnets and stacked, planar-spiral micro-coils. The new moving-coil actuator outperforms previous coil designs as it enables orthogonal and linear force capability in two axes while minimizing parasitic forces. The system performance was modeled in the structural...

Process based cost modeling of emerging optoelectronic interconnects : implications for material platform choice

Liu, Shan, S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 105 p.
ENG
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Continuously increasing demand for processing power, storage capacity, and I/O capacity in personal computing, data network, and display interface suggests that optical interconnects may soon supplant copper not only for long distance telecommunication but also for short reach connection needs. In the search for a standard, the current debate in the optoelectronic industry is focused on the technical and economic challenges of the next generation interconnect. Technological advances over the past few years have given new strength to a silicon-technology platform for optoelectronics. The possibility of extending a mature and high-yield Si CMOS manufacturing platform of the electronic industry into the optical domain is an area of intensive interest. Introducing new photonic materials and processes into the mature electronic industry involves a convergence of knowledge between the optoelectronics and semiconductor IC manufacturers. To address some of the technical, market, and organizational uncertainties with the Si platform, this research explores the economic viability and operational hurdles of manufacturing a 1310 nm, 100G Ethernet LAN transceiver. This analysis is carried out using the process-based cost modeling method. Four transceiver designs ranging from the most discrete to a high level of integration are considered on both InP and Si platforms. On the macro-level...

Formulación del plan de gestión de residuos peligrosos para los laboratorios de térmicas y de metalografía y resistencia de materiales de la facultad de ingeniería (Universidad Militar Nueva Granada, sede principal); Formulation of the plan for hazardous waste management for the laboratories of thermal and metallography and the resistance of materials of the faculty of engineering (University Military Nueva Granada, headquarters)

Peña Cañón, Diana Janeth; Ruiz Suárez, Erika Johana
Fonte: Universidad Militar Nueva Granada; Facultad de Ingeniería; Especialización en Planeación Ambiental y Manejo Integral de los Recursos Naturales Publicador: Universidad Militar Nueva Granada; Facultad de Ingeniería; Especialización en Planeación Ambiental y Manejo Integral de los Recursos Naturales
Tipo: bachelorThesis; Trabajo de grado Formato: pdf; pdf
SPA
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Debido a la preocupación del Medio Ambiente, la humanidad ha venido implementando medidas para prevenir, mitigar y corregir los impactos ambientales generados por actividades antrópicas. Por lo anterior, la UMNG por medio de su política ambiental definida en la Resolución 1877 de 2010 reafirma su compromiso para con el medio ambiente, la sociedad y por ende a las generaciones futuras. Es así, que en el presente documento se formula el plan de gestión integral de residuos peligrosos que busca mitigar los impactos ambientales generados por éstos, en las actividades realizadas en los laboratorios de térmicas y de metalografía y resistencia de materiales, residuos a los que en el momento no se les maneja adecuadamente.; Due to concerns of the Environment, humanity has been implementing measures to prevent, mitigate and remedy the environmental impacts generated by human activities. Therefore, the UMNG through its environmental policy defined in Resolution 1877 of 2010 reaffirms its commitment to the environment, society and therefore to future generations. Thus, in this paper is formulated comprehensive management plan for hazardous waste that seeks to mitigate the environmental impacts generated by them in the activities conducted in the laboratories of thermal and metallographic and strength of materials...

Validation of the material point method and plasticity with Taylor impact tests

Banerjee, Biswajit
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/01/2012
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Taylor impacts tests were originally devised to determine the dynamic yield strength of materials at moderate strain rates. More recently, such tests have been used extensively to validate numerical codes for the simulation of plastic deformation. In this work, we use the material point method to simulate a number of Taylor impact tests to compare different Johnson-Cook, Mechanical Threshold Stress, and Steinberg-Guinan-Cochran plasticity models and the vob Mises and Gurson-Tvergaard-Needleman yield conditions. In addition to room temperature Taylor tests, high temperature tests have been performed and compared with experimental data.; Comment: 21 pages, 12 figures, 2004

Referenes for tensile strength of vitreous silica at room temperature

Gretarsson, Andri M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/05/2002
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Some references for the breaking strength of fused silica fibers compiled in 1999.; Comment: 2 pages. 1 figure. Compiled in July, 1999

Formation of quantum spin Hall state on Si surface and energy gap scaling with strength of spin orbit coupling

Zhou, Miao; Ming, Wenmei; Liu, Zheng; Wang, Zhengfei; Yao, Yugui; Liu, Feng
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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For potential applications in spintronics and quantum computing, it is desirable to place a quantum spin Hall insulator [i.e., a 2D topological insulator (TI)] on a substrate while maintaining a large energy gap. Here, we demonstrate a unique approach to create the large-gap 2D TI state on a semiconductor surface, based on first-principles calculations and effective Hamiltonian analysis. We show that when heavy elements with strong spin orbit coupling (SOC) such as Bi and Pb atoms are deposited on a patterned H-Si(111) surface into a hexagonal lattice, they exhibit a 2D TI state with a large energy gap of over 0.5 eV. The TI state arises from an intriguing substrate orbital filtering effect that selects a suitable orbital composition around the Fermi level, so that the system can be matched onto a four-band effective model Hamiltonian. Furthermore, it is found that within this model, the SOC gap does not increase monotonically with the increasing strength of SOC. These interesting results may shed new light in future design and fabrication of large-gap topological quantum states.; Comment: Total 23 pages, 5 figures. Supporting information with additional 5 figures also included

A computational analysis of the vibrational absorption of molecular solids in the teraherz range

Tomerini, Daniele
Fonte: University of Cambridge; Department of Chemistry Publicador: University of Cambridge; Department of Chemistry
Tipo: Thesis; doctoral; PhD
EN
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In this thesis, we deal with the application of transmission terahertz spectroscopy as an analysis tool for the study of molecular solids, in particular organic crystals of pharmaceutical interest. Most of the work has been performed using two computational packages aimed at the interpretation of the spectra, one based on molecular forcefields (DMACRYS), the other on solid state density functional theory (CASTEP). We compare low temperature determinations of several molecular organic crystals to calculated spectra, and attempt to assign calculated modes of vibrations to absorption peaks, based on the similarity in frequency between the measured and calculated peaks. One of the main aims of this work is to establish the limits of our forcefield approach, which is based on the approximation that the intramolecular degrees of freedom can be neglected. We analyse the normal modes of vibration calculated with CASTEP, evaluating the amount of rigid molecule rotational and translational contribution to each eigenvector as a function of frequency, in order to validate our forcefield approach. We also compare the two sets of eigenvectors from the DMACRYS and CASTEP calculations to assess the similarity between the two approaches. We perform the same eigenvectors analysis on several hydrate systems in order to understand the role of water in the lattice dynamics of crystalline hydrates. We attempt a classification of the eigenvectors based on the strength of the forces involved in the molecular vibrations and based on the amount of the water contribution to each normal mode. A set of isostructural crystals is analysed in order to understand the effect that small variations (in the molecular formula and in the unit cell arrangement) have on the measured and calculated absorption spectra of a crystal. Finally...

Electrophoretic deposition of monochrome and color phosphor screens for information displays

Talbot, J.B.; Sluzky, E.; Kurinec, Santosh
Fonte: Springer Netherlands - Journal of Materials Science Publicador: Springer Netherlands - Journal of Materials Science
Tipo: Artigo de Revista Científica
EN_US
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This paper reviews our research on the electrophoretic deposition (EPD) of phosphors for the processing of monochromatic and color screens for information displays. Our investigation began with the study of the fundamentals of the EPD process for phosphors. The processing variables which enhance the adhesion strength of phosphor deposits were determined. The optical performance of phosphors deposited by EPD was shown to be not affected by the process itself nor by the conditions which enhance phosphor adhesion. Processes developed to produce high-resolution color screens by combining EPD and photolithography techniques are described. Also, a method to electrophoretically deposit phosphor in a thermo-reversible gel from mixtures of poly(butyl methacrylate) and isopropanol was examined.; RIT community members may access full-text via RIT Libraries licensed databases: http://library.rit.edu/databases/

Estimation of bore loads in quenching of rings by an expanding segmented die

Dodd, Harry
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
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The purpose of this investigation was to develop a method that could be used to estimate the necessary bore load on a part quenched in a quenching machine with an expanding segmented die. Such a method would be of special benefit to gear manufacturers with little quenching experience; and it could also help to greatly reduce or eliminate the very costly trial and error procedure presently used. The method must be simple enough to be used in a production situation. Such a method has been developed for estimating the expander cylinder force required to produce the greatest amount of correction in the out of round of a ring part with the least expansion of the bore. The theory has been developed for each portion of the procedure. Elastic deflections and stresses of the part, as predicted by the theory, have been compared with a finite element modeled part which agreed with the theory within 8%. Also, two test cases were made to determine how well the overall procedure compared with actual successful production examples, and it was found that the procedure does quite accurately predict the necessary bore loads. The limitations of the procedure and other factors not included in the procedure have been discussed.

Complex Shaped Mold Manufacturing by Means of Laminate Object Manufacturing

Marais, Joachim
Fonte: Center for Composite Materials Publicador: Center for Composite Materials
Tipo: Relatório Formato: 2084637 bytes; application/pdf
EN_US
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Complex shaped composite parts are needed for many applications. The base of every complex shaped part is a mold that represents the shape. However, the fabrication of a mold is very expensive and requires a high amount of skills, money and labor time. Therefore, a low cost, flexible and fast process is needed. Rapid prototyping processes such as Laminate Object Manufacturing (LOM) can reduce cost and time. But is this process, based on sensitive paper, can be used to build molds? The goal of this project is to evaluate the manufacturing process of a paper baser LOM mold and to improve the strength of such a mold in order to increase its durability.